The question of whether optimal body weight is the same throughout adulthood or changes with age has an important impact on the construction of recommended weight guidelines for the public. The widely used height-weight tables from the Metropolitan Life Insurance Company did not distinguish between younger and older adults. The more recent guidelines from the National Academy of Sciences give recommendations in six age groupings while the US Departments of Agriculture and Health and Human Services give weight guidelines in two age groupings. The validity of these age-specific guidelines continues to be hotly debated. Definitive studies to resolve this controversy are lacking. Previous studies of age-specific recommended weights or body mass index (BMI) have been plagued by methodologic problems or inadequate numbers with which to make meaningful estimations within age strata. The goals of this project are to determine the range of BMI associated with the lowest mortality in adults over a wide range of ages and to provide a basis to determine the need for age-specific guidelines for body weight. Existing data from the American Cancer Society's first Cancer Prevention Study will be used to examine associations between body weight and all cause and cause specific mortality within age strata. With over one million participants, the first Cancer Prevention Study was one of the largest cohort studies ever conducted in this country. This data set provides ample sample size to conduct analyses within age and gender groupings while controlling for important confounders such as smoking and disease-induced weight loss. The investigators point out that the size of the cohort and the availability of information on smoking, unintentional weight loss and other pertinent variables make this data set extremely valuable for these analyses. Using a single, traditional cutpoint to define overweight, a recent national survey has shown that the prevalence of overweight has increased sharply in this country and that the most dramatic increases have been in adults between the ages of 50 and 74. The investigators state that the research proposed here will examine whether the use of a single cutpoint at all ages is appropriate and has important implications for public health policy and goals.